To access values you need to understand the indexing, in your case it’s like that:
…[0]…[1]…[2]…[3]…
var myArray = [[1,2,3], [4,5,6], [7,8,9], [[10,11,12], 13, 14]];
…[0]…[1]…[2]
a tip i wrote down was to remember “Zero-Indexing” so therefore the first bracket would be 0, the next bracket would be 1, next bracket would be 2, etc etc…